Go to a pharmacy and ask about a complete liquid diet for someone who had jaw surgery? They should have stuff that's pretty much Soylent, but more expensive and designed and tested by experts.
Yup, and the magic search keywords here seem to be "total diet replacement".
A quick & dirty Google search returns a recent paper, which lists Optifast, KicStart, and Optislim as brands "packaged and marketed as very-low-energy diets (VLED), defined as total dietary replacement with FMR [formulated meal replacements]". The "Price per serve" of those brands, incidentally, is given as 1.87 to 2.99 AUD in table 1.
They also seem to be intended for weight loss, so you might want to augment your calories with normal, high-energy ...
Rob Rhinehart's food replacement Soylent now has a crowdfunding campaign.
If you're interested in one or more of these benefits, send in some money! There is also a new blog post.